Do birds of the same species ,such as each pigeon that we see in cities, have unique facial geometries (facial phenotypes) regardless of their feather ,colors, spots etc? Sometimes it is almost impossible to distinguish two pigeons between each other just looking at their facial structure and curvature of their heads.
Human face has evolved with countless of varieties such as shape of nose, distance between the eyes, proportion of mouth and the nose etc. Billions of humans have existed so far and billions of humans will ever exist each have unique facial features.
However some animals of the same species (birds like pigeons, baby chicks, fish species like sardines and sea bream etc) look like sharing a limited amount of variations in their facial geometries therefore they become distinguishable only because of their colors, patterns etc. I know that mammals such as apes or dogs have unique faces almost as distinctive as humans. I also know that human brain is already attuned to distinguish differences in human faces more than any other animal.
What I would like to understand whether all pigeons have existed so far and will exist furthermore have unique facial geometries like humans? Or do they all differ in millimetric level which cannot be captured by naked human eyes? Can two pigeons(or sardines) of the same species share exact same facial geometries unlike humans? I couldn't have satisfactory answers in this subject so far. Can you please explain?
